1. Field of the Invention
The present invention relates to an image forming apparatus wherein the web of a web press or the like is fed with tension applied thereto.
2. Prior Art
The following describes the general image forming apparatus with reference to FIG. 2.
In FIG. 2, the image forming apparatus 1 mainly comprises an infeed unit 2, a tension controller 3, a walk controller 4, an image forming unit 5, a fixing apparatus 6, an outfeed unit and a feed roller 8 (not illustrated in FIG. 1). Numeral 9 denotes a web where continuous paper such as rolled paper supplied in the form wound in a roll or box paper supplied in a form folded in a certain length is used. This web 9 forms a feed path xe2x80x9caxe2x80x9d running through the above stated apparatuses 2, 3, 4, 5, 6, 7 and 8 in that order.
The web 9 is straightened by a pre-processor (not illustrated) and is fed to the infeed unit 2.
To ensure high-precision feed on the image forming apparatus 1, tension is applied to the web in the area from the infeed unit 2 to the outfeed unit 7, and the web is fed under this tension. This area is provided with the tension controller 3 for ensuring stable tension and the walk controller 4 for correcting walking of the web 9 across the width.
The web 9 having its feed accuracy ensured is dried and fixed by the fixing apparatus 6 after an ink image and toner image have been transferred thereon, by the image forming unit 5. Then the web 9 is ejected out of the engine as a print output.
The image forming apparatus 1 using continuous paper requires preparatory work wherein the web 9 is routed through the feed route xe2x80x9caxe2x80x9d at the time of installation or before printing is started because of processing of the broken web 9 or others. The web can be routed by a manual method or by using a paper feed roller or a traction member.
FIG. 3 is a diagram representing an automatic paper routing technique by a paper feed roller 83, as is also shown in FIG. 2.
In FIG. 3, paper feed rollers 83 movable, as shown by a dotted line, are provided at various positions on the feed path xe2x80x9caxe2x80x9d, opposite to each feed rollers 8 forming the feed path xe2x80x9caxe2x80x9d shown in FIG. 2. These paper feed rollers 83 are configured to contact the feed rollers 8 only when paper is routed, and to feed paper along the feed path xe2x80x9caxe2x80x9d. The web 9 is gripped and fed successively by paper feed rollers 83, and is routed through the fed path xe2x80x9caxe2x80x9d.
FIG. 4 is a diagram representing an automatic paper routing technique by a traction member 84.
In FIG. 4, traction members 84 such as wire ropes are routed on both sides along the feed path xe2x80x9caxe2x80x9d of the web 9. The leading edge of the web 9 is fixed through the traction members 84 on the right and left and the traction cord, and the web 9 is routed through the feed path xe2x80x9caxe2x80x9d as it is pulled by traction members 84.
A great variety of traction based paper routing methods have been proposed.
The major point of these paper routing technique is to route the web 9 through the feed path xe2x80x9caxe2x80x9d, and only paper end guide 85 are provided for positioning of the web 9 across the width, without further effective measures being taken. These paper end guides 85 are arranged at various places on the feed path xe2x80x9caxe2x80x9d where the web 9 is routed, and the web 9 is fed under the control of these paper end guides 85.
Paper end guides 85 are arranged so that their distance will be greater than the width of the web 9. This is to ensure that they will not interrupt paper feed. So the web 9 is fed while walking to the right and left between feed guides 85.
As described above, the major point of the above stated paper routing technique is to route the web 9 through the feed path xe2x80x9caxe2x80x9d, and only paper end guide 85 are provided for positioning of the web 9 across the width. This technique fails to ensure satisfactory initial loading position accuracy for the web across the width, with the result that the web may be loaded while walking at various parts on the feed path.
When the web is loaded while walking as described above, uneven tension occurs between feed rollers if printing tension is applied to the web, and the web is broken in some cases.
Should the web remain unbroken, the bent portion is caught by various rollers if web feed is continued. As a result, the web was crumpled and paper jamming or a big walk actually occurred in some cases.
Further, if walk control is performed, the difference between initial web loading position and the target position (the position where the width direction of the web is corrected) of the walk controller is much greater than the amount of walking appearing in the normal feed. This may result in excessive working of the walk control, and uneven web tension in the lateral direction. As a result, paper was actually crumpled or broken in some cases.
An object of the present invention is to provide an image forming apparatus characterized in that the web position across the width is determined to an high accuracy before printing starts, whereby uniform tension on the right and left is ensured, and the web is prevented from being crumpled or broken.
The above stated object can be attained by the present invention by an image forming apparatus which comprises two feed means for feeding a web, tension control means arranged on between said two feed means and for giving a predetermined tension to said web, walk control means for correcting a position of a width direction of said web, an image forming means for forming an image on said web, fixing means for drying and fixing said image formed on said web, and feed rollers for constituting a feed passage in which said feed passage is arranged to pass through said web on said respective above means; the image forming apparatus, wherein a low tension feed process is provided, said low tension feed process feeds said web, before a printing, until to syusoku an initial mounting position of said width direction of said web to a target position of said walk control means, a tension of said web is restrained lower than a tension during the printing, and carries out a walk correction according to said walk control means.
The above stated object can be attained by the present invention by an image forming apparatus, wherein a web feed speed of said low tension fed process is kept lower than a feed speed during the printing.
The above object can be attained by the present invention providing an image forming apparatus comprising: feed means arranged on the upstream and downstream sides of a web feed path, tension control means arranged between these feed means in order to give a specified tension to the above stated web, walk control means for correcting the position of the above stated web across the width, image forming means for forming an image on the above stated web, and fixing means for drying and fixing the image formed on the above stated web through the above stated image forming means; the above stated image forming apparatus characterized by comprising a low tension feed process further comprising; a step for keeping the tension of the above stated web lower than that at the time of image formation until the initial loading position of the above stated web across the width reaches the target position of the above stated walk control means, and a step for feeding the above stated web while correcting walk with walk control means.
The above object can also be attained by the present invention providing an image forming apparatus wherein the above stated low tension feed process is characterized in that said web feed speed is lower than the feed speed at the time of image formation.
The above object can also be attained by the present invention providing an image forming apparatus wherein the above stated low tension feed process is characterized in that the difference in the distance between initial web loading position and target position of said walk control means is increased.
The above object can also be attained by the present invention providing an image forming apparatus characterized in that the above stated walk control means comprises a walk sensor.
The above object can also be attained by the present invention providing an image forming apparatus characterized in that the time for terminating said low tension feed process is determined by processing the reading of the above stated walk sensor.
The above object can also be attained by the present invention providing an image forming apparatus characterized in that the web feed speed of the above stated low tension feed process is lower than that at the time of image formation.